General Description: For designs with high slice utilization, a large amount of "unrelated merging" may occur. (Unrelated merging is when MAP has combined logic into the same slice that has no shared pin connectivity.) The MAP report device summary contains a listing of the number and percentage of slices that contain unrelated logic.
Slices containing unrelated logic can cause problems during placement because there may be conflicting placement needs such that there is no satisfactory location for all paths involved. The result is long routing delays for one of the paths.
For critical logic, it is possible to define a subset of the design as an area group; you can apply a pack factor of 0 to the area group to prevent any unrelated merges from affecting that logic.